The macroscopic properties of cycloolefin copolymers depend on the microstructure of the polymer chain. The microstructure of the polymer chain is influenced by the type of catalyst used.
In R. A. Wendt, G. Fink, Macromol. Chem. Phys. 2001, 202, 3490, the microstructure of ethene/norbornene copolymers which were prepared with the aid of various catalyst systems is investigated. Since norbornene generally shows only a slight tendency to block formation, alternating copolymers are formed with the use of most known catalysts with an excess of norbornene. However, examples are also described for racemically and mesomerically linked norbornene diads. For example, copolymers having racemically linked norbornene diads can be produced with the aid of the catalyst system Me2C(Cp)(Flu)ZrCl2 (Me=methyl, Cp=cyclopentadienyl, Flu=fluorenyl). Furthermore, ethene/norbornene copolymers having mesomerically linked diads, which also show signals from 34.5 to 40.5 ppm in the 13C-NMR spectrum, are produced with the aid of Me2Si[Ind]2ZrCl2 catalysts (Ind=indenyl). These signals are presumably to be assigned to norbornene triads. However, the authors did not succeed in preparing copolymers which contain racemically linked diads and also show signals from 34.5 to 40.5 ppm in the 13C-NMR spectrum.
It is therefore an object of the present invention to provide cycloolefin copolymers having a novel microstructure which have racemically linked diads of the polycyclic units and triads of the polycyclic units, and which additionally contain signals from 34.5 to 40.5 ppm for the norbornene-ethylene system in the 13C-NMR spectrum, processes for their preparation and selected catalysts which can be used in these processes.
This object is achieved by the features of the independent claims 1 and 13.
Special embodiments of the invention are defined by the subclaims.
Surprisingly, it has been found that special metallocene catalysts which show no Cs symmetry relative to the centroid-metal-centroid plane are suitable for the copolymerization of cycloolefins with 1-olefins, with the aid of which copolymers having a special microstructure can be provided.
This microstructure is characterized by the presence of racemic diads of repeating polycyclic units and additionally by further repeating polycyclic units. Racemically linked norbornene diads in ethylene-norbornene copolymers have characteristic signals in the 13C-NMR spectrum. These signals show a chemical shift of 29.44 ppm and 31.24 ppm, the solvent used being C2D2Cl4 and the average solvent signal having a chemical shift of 74.00 ppm. In the case of the additional repeating polycyclic units, it is assumed that they are racemic cycloolefin triads which, in the case of ethylene-norbornene copolymers, produce additional signals from 34.5 to 40.5 ppm in the 13C-NMR spectrum. Diads are defined as two polycyclic olefin units directly linked to one another, and triads are defined as three polycyclic olefin units directly linked to one another.
In the context of the present invention, centroid is to be understood as meaning the center of the cyclopentadienyl ring linked to the metal by complex formation. This may be a cyclopentadienyl ligand or a substituted cyclopentadienyl ligand or a ligand which has a higher degree of condensation and a cyclopentadienyl ring and which optionally may be substituted.
A plane which represents a plane of symmetry is defined by the centers of the metal atom and of the two centroids. Catalysts used in the process according to the invention have no Cs symmetry in relation to this plane.
Some of these metallocene catalysts have already been used for the polymerization of 1-olefins.
In the article “Asymmetric Zirconocene Precursors for Catalysts of Propylene Polymerisation”, Fierro, Ricardo et al., J. Polym. Sci., Part A: Polym. Chem. (1994), 32(15), 2817-24, propylene polymerization with the use of racemic isopropylidene (1-η5-cyclopentadienyl)-(η5-indenyl)-dichlorozirconium and the 3-methylindenyl derivative thereof are described. Both derivatives lead to similar products in the propylene polymerization.
JP-A-05/043619 describes the polymerization of ethene in the presence of isopropylidene(cyclopentadienyl)(indenyl)zirconium dichloride and methylaluminoxane in toluene. In the polymerization, branched polyethylene forms without addition of a comonomer.
In the article “Syndiospecific Propylene Polymerization with C1 Symmetric Group 4 ansa-Metallocene Catalysts”, Leino, Reko, et al., Macromolecules (2001), 34(7), 2072-2082, bridged and substituted cyclopentadienyl-3-R-indenylmetallocenes are described. The polymerization of propene with the aid of these catalysts leads to syndiotactic polypropylene.
JP-A-52/02124 describes the polymerization of 1-olefins in the presence of metallocene catalysts and aluminoxanes. The metallocene catalysts have a bridged cyclopentadienyl sandwich structure, one of the cyclopentadienyl rings being substituted.
“Synthesis, structure, and catalytic properties of ansa-zirconocenes, Me2X(Cp)(RInd)ZrCl2 (X═C, Si, R=2-p or 3-p-tolyl)”, Yoon, Sung Cheol et al., J. Organomet. Chem. (1997), 534(1-2), 81-87, describes novel metallocene complexes which were developed with the aim of providing catalysts for the preparation of syndiotactic polypropene. However, the synthesized complexes show only slight syndiospecificity.
The article “Syndiospecific Propylene Polymerization Using C1-Symmetric ansa-Metallocene Catalysts: Substituent and Bridge Effects”, Gomez, Fernando J., et al., Macromolecules (2002), 35(9), 3358-3368, describes the synthesis of a number of C1-symmetric ansa-metallocenes ([Me2X(Cp)(2-R1-3-R2-Ind)]ZrCl2, X═C, Si; R1=H, Me; R2=Me, Et, CH2SiMe3), and their catalytic behavior in the polymerization of propene. Depending on substituent size, substituent pattern and bridging unit, polypropylene having different high degrees of syndiotacticity ([rrrr]=28-66%) was obtained.